By Summer Orledge

Faculty Mentor: Dr. Tyler Frankel

Abstract

Anthropogenic activities such as industrial discharges, agricultural runoff, and munitions testing can often result in the enrichment of various metals beyond background levels. Many of these persistent contaminants pose neurotoxic, carcinogenic, or reproductive risks to aquatic wildlife and humans. While water chemistry is known to modulate the release of metals from sediments, few studies have been conducted to test these effects on localized environmental samples. This study evaluates how pH and hardness conditions control the distribution of 16 elements between sediment and water in contaminated surficial sediments collected from the Potomac River and Mattawoman Creek (Indian Head, MD). Sediment samples were oven-dried, sieved to 125 µm, and homogenized. Five g sediment subsamples were mixed with 100 mL deionized water adjusted to 20, 60, or 100 ppm Ca (as CaCO3) and pH 6.0, 6.5, 7.0, 7.5, or 8.0 using KOH and HCl. After 48 hours, supernatants were filtered and acidified with 300 µL HNO3. The remaining sediments were re-dried for 48hrs, sieved to 63 µm, digested in aqua regia (3H2O:3HCl:1HNO3), filtered, diluted, and analyzed for Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb, V, Zn content via Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Partitioning coefficients (Kd) were calculated as [sediment concentration]/[water concentration] and log transformed (logKd) to minimize variability. Preliminary results suggest increased Ca (p < 0.0001), Cd (p = 0.0013), Co (p < 0.0001), Mg (p < 0.0001), Mn (p < 0.0001), Ni (p < 0.0001), and Zn (p < 0.0001) mobilization in acidic conditions and Co (p = 0.0013), Cr (p = 0.026), Cu (p = 0.0005), Fe (p = 0.019), Ni (p = 0.0006), V (p = 0.026), and Zn (p = 0.0018) release in softer water (p < 0.05). This study elucidates the potential release and toxic effects of contaminated sediments on aquatic ecosystems in the Potomac River.